```html ``` 2. [Custom CSS mixins](https://github.com/PolymerElements/iron-flex-layout/blob/master/iron-flex-layout.html). The mixin stylesheet includes custom CSS mixins that can be applied inside a CSS rule using the `@apply` function. Please note that the old [/deep/ layout classes](https://github.com/PolymerElements/iron-flex-layout/tree/master/classes) are deprecated, and should not be used. To continue using layout properties directly in markup, please switch to using the new `dom-module`-based [layout classes](https://github.com/PolymerElements/iron-flex-layout/tree/master/iron-flex-layout-classes.html). Please note that the new version does not use `/deep/`, and therefore requires you to import the `dom-modules` in every element that needs to use them. A complete [guide](https://elements.polymer-project.org/guides/flex-layout) to `` is available. @group Iron Elements @pseudoElement iron-flex-layout @demo demo/index.html -->